1. Field of the Invention
The present invention relates in general to steering systems for road vehicles and more particularly to a steering system of the type equipped with an anti-rotation mechanism for holding a steering wheel center pad, etc. stationary irrespective of rotation of a steering wheel.
2. Description of the Prior Art
A steering system equipped with such an anti-rotation mechanism, as disclosed in Japanese Provisional Utility Model Publication No. 57-163448, includes a pair of upper and lower internal gears, the upper one of which is screwed to an upper end of a jacket or column of a steering column assembly and the lower one of which is rotatably mounted on a hub portion of a steering wheel. On the hub portion of the steering wheel there are fixedly mounted a plurality of brackets each of which in turn rotatably carries thereon a pinion meshed with the teeth of both the upper and lower internal gears so that upon rotation of the steering wheel, the pinions rotate about the axis thereof while at the same time revolving about the steering shaft for thereby holding the upper internal gear and a steering wheel center pad, etc. mounted on the upper internal gear stationary irrespective of rotation of the steering wheel.
In this kind of steering system, there has been a necessity of providing a suitable clearance between the upper internal gear and the hub portion for compensating for the difference in thermal expansion therebetween and thereby keeping them smoothly rotatable relative to each other at all times. The necessity of such a clearance may however lead to the problem that the axis of revolution of the pinion about the steering shaft is misaligned with the axes of rotation of the upper and lower internal gears to result in play of the upper internal gear. Furthermore, since the upper and lower internal gears, the bracket, etc. are respectively made of suitable resinous materials, variations of temperature will cause changes in engagement of the pinions and the upper and lower internal gears due to the difference in thermal expansion or contraction therebetween, resulting in further play of the upper internal gear. Since the upper internal gear is adapted to mount thereon the steering wheel center pad, etc., such play of the upper internal gear inevitably deteriorates the quality of the steering system.